Encoding method, decoding method, encoder, and decoder

ABSTRACT

An encoder includes circuitry and memory. Using the memory, the circuitry performs a primary transform on a derived prediction error, performs a secondary transform on a result of the primary transform, quantizes a result of the secondary transform, and encodes a result of the quantization as data of an image. When a current block to be processed has a predetermined shape, the encoder performs the secondary transform using, among secondary transform basis candidates that are secondary bases usable in the secondary transform, only a secondary transform basis candidate having a size that is not largest size containable in the current block.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.16/371,691, filed Apr. 1, 2019, which claims the benefit of U.S.Provisional Patent Application No. 62/651,322 filed Apr. 2, 2018. Theentire disclosures of the above-identified applications, including thespecification, drawings and claims are incorporated herein by referencein their entirety.

FIELD

The present disclosure relates to an encoder, a decoder, an encodingmethod, and a decoding method.

BACKGROUND

H.265 has conventionally been present as a standard for encoding movingpictures. H.265 is also referred to as high efficiency video coding(HEVC).

CITATION LIST Non Patent Literature

-   [NPL 1] H.265 (ISO/IEC 23008-2 HEVC)/HEVC (High Efficiency Video    Coding)

SUMMARY Technical Problem

In such an encoding method and a decoding method, there has been adesire for an increase in processing efficiency.

The present disclosure has an object to provide an encoder, a decoder,an encoding method, and a decoding method that enable an increase inprocessing efficiency.

Solution to Problem

An encoder according to one aspect of the present disclosure is anencoder that encodes moving pictures and includes circuitry and memory.Using the memory, the circuitry derives a prediction error of an imageincluded in the moving pictures by subtracting a prediction image of theimage from the image; performs a primary transform on the predictionerror, and a secondary transform on a result of the primary transform;quantizes a result of the secondary transform; when a current block tobe processed has a predetermined shape, performs the secondary transformusing, among secondary transform basis candidates that are transformbases usable in the secondary transform, only a secondary transformbasis candidate having a size that is a largest size containable in thecurrent block.

A decoder according to one aspect of the present disclosure is a decoderthat decodes moving pictures and includes circuitry and memory. Usingthe memory, the circuitry decodes data of an image included in themoving pictures; inverse quantizes the data; performs an inversesecondary transform on a result of the inverse quantization, and aninverse primary transform on a result of the inverse secondarytransform; derives the image by adding, as a prediction error of theimage, a result of the inverse primary transform to a prediction imageof the image; and when a current block to be processed has apredetermined shape, performs the inverse secondary transform using,among inverse secondary transform basis candidates that are transformbases usable in the inverse secondary transform, only an inversesecondary transform basis candidate having a size that is not a largestsize containable in the current block.

These general and specific aspects may be implemented using a system, anapparatus, a method, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, apparatuses, methods, integrated circuits, computerprograms, or computer-readable recording media.

Additional benefits and advantages of the disclosed embodiment will beapparent from the Specification and Drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the Specification and Drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

Advantageous Effects

The present disclosure provides an encoder, a decoder, an encodingmethod, and a decoding method that enable an increase in processingefficiency.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1.

FIG. 3 is a chart indicating transform basis functions for eachtransform type.

FIG. 4A illustrates one example of a filter shape used in ALF.

FIG. 4B illustrates another example of a filter shape used in ALF.

FIG. 4C illustrates another example of a filter shape used in ALF.

FIG. 5A illustrates 67 intra prediction modes used in intra prediction.

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing.

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing.

FIG. 5D illustrates one example of FRUC.

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory.

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture.

FIG. 8 is for illustrating a model assuming uniform linear motion.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks.

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1.

FIG. 11 is a diagram for illustrating secondary transform.

FIG. 12 is a flow chart indicating an example of internal processing oftransformer 106 in encoder 100 according to a first aspect of Embodiment1.

FIG. 13A is a table indicating an example of the number of requiredtimes the primary transform according to the first aspect of Embodiment1 is performed.

FIG. 13B is a table indicating an example of the number of requiredtimes the secondary transform according to the first aspect ofEmbodiment 1 is performed.

FIG. 14 is a table indicating an amount of processing required toprocess an entire CTU for each block size according to a comparativeexample.

FIG. 15 is a table indicating an amount of processing required toprocess an entire CTU for each block size according to the first aspectof Embodiment 1.

FIG. 16 is a block diagram illustrating an implementation example of theencoder according to Embodiment 1.

FIG. 17 is a flow chart indicating an operation example performed by theencoder according to Embodiment 1.

FIG. 18 is a block diagram illustrating an implementation example of thedecoder according to Embodiment 1.

FIG. 19 is a flow chart indicating an operation example performed by thedecoder according to Embodiment 1.

FIG. 20 illustrates an overall configuration of a content providingsystem for implementing a content distribution service.

FIG. 21 illustrates one example of an encoding structure in scalableencoding.

FIG. 22 illustrates one example of an encoding structure in scalableencoding.

FIG. 23 illustrates an example of a display screen of a web page.

FIG. 24 illustrates an example of a display screen of a web page.

FIG. 25 illustrates one example of a smartphone.

FIG. 26 is a block diagram illustrating a configuration example of asmartphone.

DESCRIPTION OF EMBODIMENTS

For example, an encoder according to one aspect of the presentdisclosure is an encoder that encodes moving pictures and includescircuitry and memory. Using the memory, the circuitry derives aprediction error of an image included in the moving pictures bysubtracting a prediction image of the image from the image; performs aprimary transform on the prediction error, and a secondary transform ona result of the primary transform; quantizes a result of the secondarytransform; when a current block to be processed has a predeterminedshape, performs the secondary transform using, among secondary transformbasis candidates that are transform bases usable in the secondarytransform, only a secondary transform basis candidate having a size thatis a largest size containable in the current block.

With this, the encoder can reduce an amount of processing by transform.Accordingly, the encoder can enable an increase in processingefficiency.

Moreover, for example, when the secondary transform basis candidates arecapable of being recognized by a decoder, the circuitry may change anencoding method for the secondary transform basis candidate used in thesecondary transform, according to a number to which the secondarytransform basis candidates are narrowed down due to the predeterminedshape of the current block.

Moreover, for example, the predetermined shape may be selected from aplurality of shapes.

Moreover, for example, the predetermined shape may be specified by usinga length of a side or a ratio between a short side and a long side.

Moreover, for example, the predetermined shape may be a rectangle.

Moreover, for example, the predetermined shape may be identical to ashape of a secondary transform basis candidate having the largest sizeamong the secondary transform basis candidates.

Moreover, for example, when the shape of the secondary transform basiscandidate is 4×4 or 8×8, the predetermined shape may be 8×8.

Moreover, for example, the shape of the secondary transform basiscandidate may be a square or a shape other than the square.

A decoder according to one aspect of the present disclosure is a decoderthat decodes moving pictures and includes circuitry and memory. Usingthe memory, the circuitry decodes data of an image included in themoving pictures; inverse quantizes the data; performs an inversesecondary transform on a result of the inverse quantization, and aninverse primary transform on a result of the inverse secondarytransform; derives the image by adding, as a prediction error of theimage, a result of the inverse primary transform to a prediction imageof the image; and when a current block to be processed has apredetermined shape, performs the inverse secondary transform using,among inverse secondary transform basis candidates that are transformbases usable in the inverse secondary transform, only an inversesecondary transform basis candidate having a size that is not a largestsize containable in the current block.

With this, the decoder can reduce an amount of processing by transform.Accordingly, the decoder can enable an increase in processingefficiency.

Moreover, when the inverse secondary transform basis candidates arecapable of being obtained by an encoder, the circuitry may change adecoding method for the inverse secondary transform basis candidate usedin the inverse secondary transform, according to a number to which theinverse secondary transform basis candidates are narrowed down by theencoder.

Moreover, for example, the predetermined shape may be selected from aplurality of shapes.

Moreover, for example, the predetermined shape may be specified by usinga length of a side or a ratio between a short side and a long side.

Moreover, for example, the predetermined shape may be a rectangle.

Moreover, for example, the predetermined shape may be identical to ashape of an inverse secondary transform basis candidate having thelargest size among the inverse secondary transform basis candidates.

Moreover, for example, when the shape of the inverse secondary transformbasis candidate is 4×4 or 8×8, the predetermined shape may be 8×8.

Moreover, for example, the shape of the inverse secondary transformbasis candidate may be a square or a shape other than the square.

An encoding method according to one aspect of the present disclosure isan encoding method of encoding moving pictures. The encoding methodincludes: deriving a prediction error of an image included in the movingpictures by subtracting a prediction image of the image from the image;performing a primary transform on the prediction error, and a secondarytransform on a result of the primary transform; quantizing a result ofthe secondary transform; encoding a result of the quantization as dataof the image; and when a current block to be processed has apredetermined shape, performing the secondary transform using, amongsecondary transform basis candidates that are transform bases usable inthe secondary transform, only a secondary transform basis candidatehaving a size that is not a largest size containable in the currentblock.

With this, the encoding method can reduce an amount of processing bytransform. Accordingly, the encoding method can enable an increase inprocessing efficiency.

A decoding method according to one aspect of the present disclosure is adecoding method of decoding moving pictures. The decoding methodincludes: decoding data of an image included in the moving pictures;inverse quantizing the data; performing an inverse secondary transformon a result of the inverse quantization, and an inverse primarytransform on a result of the inverse secondary transform; deriving theimage by adding, as a prediction error of the image, a result of theinverse primary transform to a prediction image of the image; and when acurrent block has a predetermined shape, performing the inversesecondary transform using, among inverse secondary transform basiscandidates that are transform bases usable in the inverse secondarytransform, only an inverse secondary transform basis candidate having asize that is not a largest size containable in the current block.

With this, the decoding method can reduce an amount of processing bytransform. Accordingly, the decoding method can enable an increase inprocessing efficiency.

These general and specific aspects may be implemented using a system, anapparatus, a method, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, apparatuses, methods, integrated circuits, computerprograms, or computer-readable recording media.

Hereinafter, embodiments will be described with reference to thedrawings.

Note that the embodiments described below each show a general orspecific example. The numerical values, shapes, materials, components,the arrangement and connection of the components, steps, order of thesteps, etc., indicated in the following embodiments are mere examples,and therefore are not intended to limit the scope of the claims.Therefore, among the components in the following embodiments, those notrecited in any of the independent claims defining the most genericinventive concepts are described as optional components.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according toEmbodiment 1, substituting a component corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented processesperformed by one or more components included in the encoder or thedecoder according to Embodiment 1, such as addition, substitution, orremoval, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processescorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosure;

(4) combining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) combining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1 , encoder 100 is a device that encodes apicture block by block, and includes splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, block memory 118, loop filter120, frame memory 122, intra predictor 124, inter predictor 126, andprediction controller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in the present embodiment, there isno need to differentiate between CU, PU, and TU; all or some of theblocks in a picture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2 , the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2 , block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2 , one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3 , N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPTL 1).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6 , in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7 , in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8 , (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.MATH. 1∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

$\begin{matrix}{{MATH}.\mspace{14mu} 2} & \; \\\{ \begin{matrix}{v_{x} = {{\frac{( {v_{1x} - v_{0x}} )}{w}x} - {\frac{( {1_{1y} - v_{0y}} )}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{( {v_{1y} - v_{0y}} )}{w}x} + {\frac{( {v_{1x} - v_{0x}} )}{w}y} + v_{0y}}}\end{matrix}  & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the LO direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the Li direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10 , decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[Description of Secondary Transform]

For example, transformer 106 of encoder 100 performs a transform on aprediction error, and a re-transform on the result of the transform.Then, quantizer 108 of encoder 100 quantizes the result of there-transform. A transform performed on a prediction error is alsoreferred to as a primary transform. A re-transform performed on theresult of the primary transform is also referred to as a secondarytransform. In other words, transformer 106 performs a primary transformon a prediction error, and a secondary transform on the result of theprimary transform.

More specifically, transformer 106 performs the primary transform on theprediction error using a primary transform basis. Transformer 106performs the secondary transform on the result of the primary transformusing a secondary transform basis. A primary transform basis is atransform basis used by the primary transform, and a secondary transformbasis is a transform basis used by the secondary transform. It should benoted that a transform basis includes data patterns. Each data patternmay be referred to as a basis. In this case, the transform basis may beregarded as a basis set including bases.

Decoder 200 performs operations corresponding to those of encoder 100.Specifically, inverse transformer 206 of decoder 200 performs an inversesecondary transform on the result of inverse quantization using aninverse secondary transform basis. Further, inverse transformer 206performs an inverse primary transform on the result of the inversesecondary transform using an inverse primary transform basis. Here, theinverse primary transform is a transform inverse of the primarytransform. Decoder 200 derives data before the primary transform fromdata after the primary transform by performing the inverse primarytransform using the inverse primary transform basis. The inverse primarytransform basis is a transform basis for the inverse primary transform,and a transform basis equivalent to the primary transform basis.

Specifically, decoder 200 may perform the inverse primary transform byfollowing an inverse procedure of the primary transform, using theinverse primary transform basis equivalent to the primary transformbasis.

Moreover, the inverse secondary transform is a transform inverse of thesecondary transform. Decoder 200 derives data before the secondarytransform from data after the secondary transform by performing theinverse secondary transform using the inverse secondary transform basis.The inverse secondary transform basis is a transform basis for theinverse secondary transform, and a transform basis equivalent to thesecondary transform basis.

Specifically, decoder 200 may perform the inverse secondary transform byfollowing an inverse procedure of the secondary transform, using theinverse secondary transform basis equivalent to the secondary transformbasis.

The result of the inverse quantization in decoder 200 is equivalent tothat of the secondary transform in encoder 100. In other words, theresult of the inverse quantization is equivalent to component valuesderived from the result of the primary transform, and component valuesfor the data patterns of the secondary transform basis. For example,when inverse transformer 206 performs the inverse secondary transform onthe result of the inverse quantization, inverse transformer 206 derivesthe result of the primary transform by combining the component valuesusing the inverse secondary transform basis.

Accordingly, the result of the inverse secondary transform is equivalentto the result of the primary transform in encoder 100. In other words,the result of the inverse secondary transform is equivalent to componentvalues derived from a prediction image, and component values for thedata patterns of the primary transform basis. For example, when inversetransformer 206 performs the inverse primary transform on the result ofthe inverse secondary transform, inverse transformer 206 derives theprediction error by combining the component values using the inversetransform basis.

FIG. 11 is a diagram for illustrating secondary transform. Thoughdescribed above, the secondary transform is a transform performed on asignal indicating the prediction error on which the primary transform isperformed. Here, the primary transform and the secondary transform mayeach be either a separable transform or a non-separable transform.

An area in which the secondary transform is performed may be differentfrom an area in which the primary transform is performed. For examples,as illustrated in FIG. 11 , when the primary transform is performed onan entire block, the secondary transform may be performed on only asub-block on a low frequency side among sub-blocks included in theblock.

It should be noted that the size of the sub-block on which the secondarytransform is performed need not be a fixed value, and may be changeddepending on, for example, the size of the block on which the primarytransform is performed.

There may be secondary transform basis candidates that are transformbases usable in the secondary transform. For example, there may be atotal of six secondary transform basis candidates: a first 4×4 basis, asecond 4×4 basis, and a third 4×4 basis each having a shape of 4×4, anda first 8×8 basis, a second 8×8 basis, and a third 8×8 basis each havinga shape of 8×8.

Likewise, there may be inverse secondary transform basis candidates thatare transform bases usable in the inverse secondary transform. Forexample, the encoder may write into a bitstream information such astypes of basis for identifying an inverse secondary transform basiscandidate selected and used from the inverse secondary transform basiscandidates.

Moreover, the secondary transform basis candidates may be narrowed downaccording to a given encoding parameter such as a block on which theprimary transform is performed or the size of a block to be processed bythe secondary transform. For example, when the length of a short side ofthe block to be processed is at least 8, a secondary transform basiscandidate that is a basis having a shape of 8×8 may be used among thesecondary transform basis candidates. Also, for example, when the lengthof the short side of the block to be processed is 4, a secondarytransform basis candidate that is a basis having a shape of 4×4 may beused among the secondary transform basis candidates.

[First Aspect of Transform]

Although the following mainly describes encoder 100 as an example,decoder 200 operates in the same manner as encoder 100. In particular,inverse transformer 206 of decoder 200 operates in the same manner astransformer 106 of encoder 100. For example, the transform, primarytransform, secondary transform, primary transform basis, secondarytransform basis, etc. in the following description may be appropriatelyinterchangeable with the inverse transform, inverse primary transform,inverse secondary transform, inverse primary transform basis, inversesecondary transform basis, etc.

However, inverse transformer 206 of decoder 200 performs the inverseprimary transform after the inverse secondary transform. Encoder 100encodes information, and decoder 200 decodes the information. Forexample, when encoder 100 selects a transform basis according to, forexample, an encoding load and a difference between an original image anda reconstructed image, encoder 100 may encode the information of thetransform basis, and decoder may decode the information of the transformbasis.

(Internal Configuration of Transformer in Encoder)

FIG. 12 is a flow chart indicating an example of internal processing oftransformer 106 in encoder 100 according to a first aspect of Embodiment1.

First, transformer 106 in encoder 100 determines whether a current blockhas a predetermined shape (S101).

Here, the predetermined shape is, for example, a rectangle. Thepredetermined shape is not limited to a rectangle, and may be a squareor a shape other than those. Moreover, the predetermined shape may bespecified using the length of a side. For example, the length of bothsides of the current block is 8 or at most 8. Furthermore, thepredetermined shape may be specified using a ratio between the shortside and long side of the current block. Moreover, the predeterminedshape may be specified by a block size of 8×8 or a block size other thanthe block size of 8×8, such as 16×16 or 4×4. It should be noted that thepredetermined shape may be selected from multiple shapes, such as 8×8and 16×16.

When the current block is determined to have the predetermined shape instep S101 (YES in S101), transformer 106 selects, from secondarytransform basis candidates, only a secondary transform basis candidatehaving a size that is not the largest size containable in the currentblock as a secondary transform basis used in the secondary transform(S102). It should be noted that since a size such as the largest sizespecifies a shape, the size may be interchangeable with a shape. Thesame applies in the following description.

Next, transformer 106 performs the secondary transform using only thesecondary transform basis candidate selected in step S102 (S103). Inother words, transformer 106 performs the secondary transform using thesecondary transform basis candidate narrowed down by step S102.

In contrast, when the current block is determined to not have thepredetermined shape in step S101 (NO in S101), transformer 106 selects,from the secondary transform basis candidates, a secondary transformbasis candidate having the largest size containable in the current blockas the secondary transform basis used in the secondary transform (S104).Then, transformer 106 may perform the secondary transform using only thesecondary transform basis candidate selected in step S104.

Hereinafter, the narrowing down of the secondary transform basiscandidates in the present aspect will be described using specificexamples.

First Example

It is assumed that, for example, there are a total of six secondarytransform basis candidates: a first 4×4 basis, a second 4×4 basis, athird 4×4 basis, a first 8×8 basis, a second 8×8 basis, and a third 8×8basis. In addition, it is assumed that a predetermined shape isspecified as “the length of both sides being 8.”

In such a case, when a current block has, for example, a block size of4×4, transformer 106 determines that the current block does not have thepredetermined shape in step S101. Then, transformer 106 selects thefirst 4×4 basis, the second 4×4 basis, and the third 4×4 basis assecondary transform basis candidates in step S104.

Moreover, when the current block has, for example, a block size of 8×8,transformer 106 determines that the current block has the predeterminedshape in step S101. Then, transformer 106 selects the first 4×4 basis,the second 4×4 basis, and the third 4×4 basis as secondary transformbasis candidates in step S102. As described above, transformer 106selects not 8×8 bases (the first 8×8 basis, the second 8×8 basis, thethird 8×8 basis) that are the largest size containable in the currentblock, but the first 4×4 basis, the second 4×4 basis, and the third 4×4basis.

Furthermore, when the current block has, for example, a block size of16×16, transformer 106 determines that the current block does not havethe predetermined shape in step S101. Then, transformer 106 selects thefirst 8×8 basis, the second 8×8 basis, and the third 8×8 basis, whichare the largest size containable in the current block, as secondarytransform basis candidates in step S104.

It should be noted that in the above-described first example, thesecondary transform basis candidates are narrowed down from 6 to 3. Insuch a case, an encoding method and a decoding method in which apossible value ranges from 0 to 2 may be performed.

Accordingly, for example, when a predetermined block shape is defined ina standard or information about the predetermined block shape is writtenin a bitstream, decoder 200 can recognize the predetermined block shape.In this case, since decoder 200 can recognize the predetermined blockshape and secondary transform basis candidates, encoder 100 may changean encoding method for a secondary transform basis used by the secondarytransform, according to a number to which the secondary transform basiscandidates are narrowed down due to the current block having thepredetermined shape. Moreover, in this case, when decoder 200 can obtainthe secondary transform basis candidates, decoder 200 may change adecoding method for an inverse secondary transform basis used by theinverse secondary transform, according to a number to which the inversesecondary transform basis candidates are narrowed down by encoder 100.

Second Example

It is also assumed that, for example, there are a total of ninesecondary transform basis candidates: a first 2×2 basis, a second 2×2basis, and a third 2×2 basis that have a shape of 2×2; a first 4×4basis, a second 4×4 basis, and a third 4×4 basis; and a first 8×8 basis,a second 8×8 basis, and a third 8×8 basis. In addition, it is assumedthat a predetermined shape is specified as “the length of both sidesbeing at most 8.”

In such a case, when a current block has, for example, a block size of4×4, transformer 106 determines that the current block has thepredetermined shape in step S101. Then, transformer 106 selects thefirst 2×2 basis, the second 2×2 basis, and the third 2×2 basis assecondary transform basis candidates in step S102. As described above,transformer 106 selects not 4×4 bases (the first 4×4 basis, the second4×4 basis, the third 4×4 basis) that are the largest size containable inthe current block, but the first that have the 2×2 basis, the second 2×2basis, and the third 2×2 basis.

Moreover, when the current block has, for example, a block size of 8×8,transformer 106 determines that the current block has the predeterminedshape in step S101. Then, transformer 106 selects the first 4×4 basis,the second 4×4 basis, and the third 4×4 basis as secondary transformbasis candidates in step S102. As described above, transformer 106selects not 8×8 bases (the first 8×8 basis, the second 8×8 basis, thethird 8×8 basis) that are the largest size containable in the currentblock, but the first 4×4 basis, the second 4×4 basis, and the third 4×4basis.

Furthermore, when the current block has, for example, a block size of16×16, transformer 106 determines that the current block does not havethe predetermined shape in step S101. Then, transformer 106 selects thefirst 8×8 basis, the second 8×8 basis, and the third 8×8 basis, whichare the largest size containable in the current block, as secondarytransform basis candidates in step S104.

It should be noted that in the present aspect, the predetermined shapeis not limited to the above-described shapes. For example, thepredetermined shape may be specified as the same size as a secondarytransform basis candidate having the largest size among secondarytransform basis candidates. Moreover, for example, when the shape of asecondary transform basis candidate is possibly 4×4 and 8×8, thepredetermined shape may be specified as 8×8. When the shape of asecondary transform basis candidate is possibly 2×2 and 4×4, thepredetermined shape may be specified as 4×4.

Furthermore, although the case has been described above in which whenthe current block has the predetermined shape, a secondary transformbasis candidate having the next largest size is selected as only thesecondary transform basis candidate having the size that is not thelargest size containable in the current block, the present aspect is notlimited to this. A secondary transform basis candidate having thesmallest size may be selected from secondary transform basis candidates.For example, when the smallest size among the secondary transform basiscandidates is 4×4, and the predetermine shape is a block size of 8×8, asecondary transform basis candidate having a size of 4×4 may be selectedwhen the current block has the block size of 8×8. Moreover, for example,when the smallest size among the secondary transform basis candidates is2×2, and the predetermine shape is specified as the block size of 8×8, asecondary transform basis candidate having a size of 2×2 may be selectedwhen the current block has a block size of 8×8.

It is a matter of course that when the current block has thepredetermined shape, a secondary transform basis candidate having thenext largest size may be selected from secondary transform basiscandidates containable in the current block.

For example, when the sizes of secondary transform basis candidates are4×4, 8×8, and 16×16, and the predetermined shape is specified as theblock size of 8×8, a secondary transform basis candidate having the sizeof 4×4 may be selected when the current block has the block size of 8×8.It should be noted that, for example, since the current block does nothave the predetermined shape when the current block has the block sizeof 8×8, the secondary transform basis candidate having the size of 4×4may be selected.

Likewise, for example, when the predetermined shape is specified as ablock size of 16×16, a secondary transform basis candidate having thesize of 8×8 is selected when the current block has the block size of16×16. It should be noted that, for example, when the current block hasthe block size of 8×8, a secondary transform basis candidate having thesize of 8×8 may be selected.

[Advantageous Effect of First Aspect]

The configuration of the first aspect can reduce an amount of processingby transform.

Here, an amount of processing required to process an entire coding treeunit (CTU).

FIG. 13A is a table indicating an example of the number of requiredtimes the primary transform according to the first aspect of Embodiment1 is performed. FIG. 13B is a table indicating an example of the numberof required times the secondary transform according to the first aspectof Embodiment 1 is performed. FIG. 14 is a table indicating an amount ofprocessing required to process an entire CTU for each block sizeaccording to a comparative example. FIG. 15 is a table indicating anamount of processing required to process an entire CTU for each blocksize according to the first aspect of Embodiment 1.

First, the amount of processing required to process the entire CTU canbe expressed by an amount of processing by the primary transform and anamount of processing by the secondary transform.(Amount of processing required to process entire CTU)={(Amount ofprocessing by primary transform)+(Amount of processing by secondarytransform)}×(Number of blocks contained in CTU)

Next, it is assumed that a current block is a square having a size of apower of 2 ranging from 4×4 to 32×32. In addition, it is assumed that,as illustrated in FIG. 13A and FIG. 13B, the number of required timeseach of the primary transform and the secondary transform is performedis specified for each block size. It should be noted that the number oftimes may be interpreted as the number of times multiplication isperformed, the number of times addition is performed, the sum of thesenumbers, etc.

In the example illustrated in FIG. 13B, the size of a sub-block (thesize of a secondary transform basis) on which the secondary transform isperformed is 4×4 or 8×8 as a candidate.

Here, it is assumed that only a secondary transform basis having thelargest size (shape) containable in a current block is selected as asecondary transform basis candidate in the comparative example. In thiscase, when the current block is a 4×4 block, the secondary transform isperformed on a 4×4 sub-block, and when the current block is a 8×8 blockor a larger block, the secondary transform is performed on a 8×8sub-block.

Assuming that the size of the CTU is 128×128, an amount of processingrequired when 4×4 blocks are laid over the CTU is calculated as(48+256)×{(128/4)²}=311296 times.

The same calculation can be made for other block sizes. As a result, theamount of processing required to process the entire CTU for each blocksize according to the comparative example is calculated as illustratedin FIG. 14 .

When 8×8 blocks are overlaid over the CTU, that is, when only asecondary transform basis having the largest size containable in thecurrent block is selected as a secondary transform basis candidate, itis clear that the amount of processing required to process the entireCTU is largest.

Next, it is assumed that a secondary transform basis is selected as asecondary transform basis candidate as described in the present aspect.Specifically, when a current block has a predetermined shape specifiedas the block size of 8×8, only a secondary transform basis having a sizethat is not the largest (shape) containable in the current block isselected and used as a secondary transform basis candidate, fromsecondary transform basis candidates. When that is not the case, thatis, when the current block does not have the predetermined shape, asecondary transform basis having the largest size (shape) containable inthe current block is selected and used as the secondary transform basiscandidate.

When the predetermined shape is specified as the block size of 8×8, anamount of processing required to process the entire CTU for each blocksize according to the first aspect is calculated as illustrated in FIG.15 . It should be noted that FIG. 15 shows the results of calculationmade by the same method of calculation as in FIG. 14 .

As illustrated in FIG. 15 , when the predetermined shape is specified asthe block size of 8×8, it is clear that the amount of processingrequired to process the entire CTU is largest when 32×32 blocks are laidover the CTU. Moreover, it is clear that this largest amount ofprocessing is less than half of the largest amount of processing in thecomparative example shown in FIG. 14 . Accordingly, the reduction of theamount of processing required to process the entire CTU can produce aneffect of reducing a processing delay.

As described above, since the present aspect can reduce the amount ofprocessing by transform, an encoder, a decoder, an encoding method, anda decoding method that enable an increase in processing efficiency canbe achieved.

It should be noted that not all of the components described in the firstaspect are always required, and only some of the components described inthe first aspect may be included.

[Variations]

The present disclosure is not limited to the first aspect, and thefollowing cases may be included in the scope of the present disclosure.

For example, when a block splitting structure is independent of lumasignals and chroma signals, the present disclosure may be applied toonly the luma signals or the chroma signals.

Moreover, the processing described in the first aspect may be performedor not be performed on a per slice basis or tile basis.

Moreover, the processing described in the first aspect may be performedor not be performed according to a type of slice such as I slice, Pslice, and B slice.

Moreover, the processing described in the first aspect may be performedor not be performed according to a prediction mode such as intraprediction, inter prediction, a normal mode, and a merge mode.

Moreover, a flag indicating that the processing described in the firstaspect is performed may be written into a syntax such as a sequencelayer, a picture layer, and a slice layer.

Moreover, there may be multiple predetermined shapes for use in thedetermination of the processing described in the first aspect. Forexample, predetermined shapes may be specified as the block size of 4×4and the block size of 8×8. In this case, when a current block has thepredetermined shapes of 4×4 and/or 8×8, transformer 106 selects anduses, from secondary transform basis candidates, only a secondarytransform basis candidate having a size that is not the largest size(shape) containable in the 8×8 and/or 8×8 block. In contrast, when thecurrent block does not have the predetermine shape of 4×4 or 8×8,transformer 106 may select and use a secondary transform basis candidatehaving the largest size (shape) containable in the current block.

It should be noted that a method of determining a secondary transformbasis candidate, which is different from the first aspect, may becombined with the first aspect and used. For example, a method ofdetermining a secondary transform basis candidate using an intraprediction mode may be combined with the first aspect and used.

Moreover, although the secondary transform basis candidate is selectedaccording to the size of the secondary transform basis candidate in thefirst aspect, a secondary transform basis candidate may be selected notaccording to the size of the secondary transform basis candidate butdirectly using an amount of processing.

Moreover, although the current block is a square in the exampledescribed in the first aspect, the current block may be not a squarebut, for example, a rectangle. Furthermore, although the predeterminedshape is a square in the example described in the first aspect, thepredetermined shape may be not a square but, for example, a rectangle.Likewise, although the shape (size) of the secondary transform basis isa square in the example described in the first aspect, the shape may benot a square but, for example, a rectangle.

[Implementation Example of Encoder]

FIG. 16 is a block diagram illustrating an implementation example ofencoder 100 according to Embodiment 1. Encoder 100 includes circuitry160 and memory 162. For example, the plurality of components included inencoder 100 illustrated in FIG. 1 are implemented by circuitry 160 andmemory 162 illustrated in FIG. 16 .

Circuitry 160 is a circuit which performs information processing, and iscapable of accessing memory 162. For example, circuitry 160 is adedicated or general purpose electronic circuit which encodes video.Circuitry 160 may be a processor such as a CPU. Alternatively, circuitry160 may be an aggregation of a plurality of electronic circuits. Inaddition, for example, circuitry 160 may perform functions of aplurality of components other than components for storing information,among the plurality of components of encoder 100 illustrated in FIG. 1 ,etc.

Memory 162 is dedicated or general purpose memory in which informationfor encoding video by circuitry 160 is stored. Memory 162 may be anelectronic circuit, or may be connected to circuitry 160. Alternatively,memory 162 may be included in circuitry 160. Furthermore, memory 162 maybe an aggregation of a plurality of electronic circuits. In addition,memory 162 may be a magnetic disk, an optical disk, etc. or may berepresented as storage, a recording medium, or the like. In addition,memory 162 may be non-volatile memory, or volatile memory.

For example, in memory 162, video to be encoded may be stored or abitstream corresponding to encoded video may be stored. In addition, aprogram to be executed by circuitry 160 for encoding video may be storedin memory 162.

In addition, for example, memory 162 may perform functions of acomponent for storing information, among the plurality of components ofencoder 100 illustrated in FIG. 1 , etc. Specifically, memory 162 mayperform functions of block memory 118 and frame memory 122 illustratedin FIG. 1 . More specifically, reconstructed blocks, reconstructedpictures, etc. may be stored in memory 162.

It should be noted that, in encoder 100, not all the plurality ofcomponents illustrated in FIG. 1 , etc. may be mounted, or not all theplurality of processes described above may be performed. Part of theplurality of components illustrated in FIG. 1 , etc. may be included inone or more other devices, and part of the plurality of processesdescribed above may be performed by the one or more other devices. Inencoder 100, part of the components illustrated in FIG. 1 , etc. ismounted, and part of the plurality of processes described above isperformed, thereby improving the processing efficiency.

Hereinafter, an example of operations performed by encoder 100illustrated in FIG. 16 will be described. In the example of operationsdescribed below, FIG. 17 is a flow chart indicating examples ofoperations performed by encoder 100 illustrated in FIG. 16 . Forexample, encoder 100 illustrated in FIG. 16 performs operationsillustrated in FIG. 17 when encoding video.

More specifically, circuitry 160 of encoder 100 performs, using memory162, processing as indicated below. In other words, first, circuitry 160derives a prediction error of an image included in video by subtractinga prediction image of the image from the image (S311). Next, circuitry160 performs a primary transform on the prediction error derived in stepS311 (S312). Next, when a current block has a predetermined shape,circuitry 160 performs a secondary transform on the result of theprimary transform performed in step S312, using, among secondarytransform basis candidates that are transform bases usable in thesecondary transform, only a secondary transform basis candidate having asize that is not the largest size containable in the current block(S313). Next, circuitry 160 quantizes the result of the secondarytransform performed in step S313 (S314). Finally, circuitry 160 encodes,as the data of the image, the result of the quantization performed instep S314 (S315).

Accordingly, encoder 100 can reduce an amount of processing bytransform, thereby enabling an increase in processing efficiency.

[Implementation Example of Decoder]

FIG. 18 is a block diagram illustrating an implementation example ofdecoder 200 according to Embodiment 1. Decoder 200 includes circuitry260 and memory 262. For example, the plurality of components included indecoder 200 illustrated in FIG. 10 are implemented by circuitry 260 andmemory 262 illustrated in FIG. 18 .

Circuitry 260 is a circuit which performs information processing, and iscapable of accessing memory 262. For example, circuitry 260 is adedicated or general purpose electronic circuit which decodes video.Circuitry 260 may be a processor such as a CPU. Alternatively, circuitry260 may be an aggregation of a plurality of electronic circuits. Inaddition, for example, circuitry 260 may perform functions of aplurality of components other than components for storing information,among the plurality of components of decoder 200 illustrated in FIG. 10, etc.

Memory 262 is dedicated or general purpose memory in which informationfor decoding video by circuitry 260 is stored. Memory 262 may be anelectronic circuit, or may be connected to circuitry 260. Alternatively,memory 262 may be included in circuitry 260. Furthermore, memory 262 maybe an aggregation of a plurality of electronic circuits. In addition,memory 262 may be a magnetic disk, an optical disk, etc. or may berepresented as storage, a recording medium, or the like. In addition,memory 262 may be non-volatile memory, or volatile memory.

For example, a bitstream corresponding to encoded video or videocorresponding to a decoded bitstream may be stored in memory 262. Inaddition, a program to be executed by circuitry 260 for decoding videomay be stored in memory 262.

In addition, for example, memory 262 may perform functions of acomponent for storing information, among the plurality of components ofdecoder 200 illustrated in FIG. 10 , etc. More specifically, memory 262may perform functions of block memory 210 and frame memory 214illustrated in FIG. 10 . More specifically, reconstructed blocks,reconstructed pictures, etc. may be stored in memory 262.

It should be noted that, in decoder 200, not all the plurality ofcomponents illustrated in FIG. 10 , etc. may be mounted, or not all theplurality of processes described above may be performed. Part of theplurality of components illustrated in FIG. 10 , etc. may be included inone or more other devices, and part of the plurality of processesdescribed above may be performed by the one or more other devices. Indecoder 200, part of the plurality of components illustrated in FIG. 10, etc. is mounted, and motion compensation is efficiently performed bymeans of part of the above-described processes being executed.

Hereinafter, an example of operations performed by decoder 200illustrated in FIG. 18 will be described. FIG. 19 is a flowchartillustrating an example of operations performed by decoder 200illustrated in FIG. 18 . For example, decoder 200 illustrated in FIG. 18performs operations illustrated in FIG. 19 when decoding video.

More specifically, circuitry 260 of decoder 200 performs, using memory262, processing as indicated below. In other words, first, circuitry 260decodes the data of an image included in video (S411). Next, circuitry260 inverse quantizes the data decoded in step S413 (S412). Next,circuitry 260 performs, using memory 262, an inverse secondary transformon the result of the inverse quantization performed in step S412 (S413).More specifically, when a current block has a predetermined shape,circuitry 260 performs the inverse secondary transform using, amonginverse secondary transform basis candidates that are inverse secondarytransform bases usable in the inverse secondary transform, only aninverse secondary transform basis candidate having a size that is notthe largest size containable in the current block. Next, circuitry 260performs an inverse primary transform on the result of the inversesecondary transform performed in step S413 (S414). Finally, circuitry260 derives the image by adding, as the result of the inverse primarytransform, the prediction error of the image to a prediction image ofthe image (S415).

Accordingly, decoder 200 can reduce an amount of processing bytransform, thereby enabling an increase in processing efficiency.

[Supplements]

Encoder 100 and decoder 200 according to the present embodiment may beused as an image encoder and an image decoder, respectively, or as avideo encoder and a video decoder, respectively. Alternatively, each ofencoder 100 and decoder 200 can be used as an intra prediction apparatus(intra-picture prediction apparatus.

In other words, encoder 100 and decoder 200 may correspond only to intrapredictor (intra-picture predictor) 124 and intra predictor(intra-picture predictor) 216, respectively. In addition, othercomponents such as transformer 106 and inverse transformer 206 may beincluded in another apparatus.

It should be noted that, each of the components in the presentembodiment may be configured in the form of an exclusive hardwareproduct, or may be realized by executing a software program suitable forthe components. Each of the components may be realized by means of aprogram executing unit, such as a CPU and a processor, reading andexecuting the software program recorded on a recording medium such as ahard disk or a semiconductor memory.

More specifically, each of encoder 100 and decoder 200 may includeprocessing circuitry and storage which is electrically connected to theprocessing circuitry and accessible from the processing circuitry. Forexample, the processing circuitry corresponds to circuitry 160 or 260,and the storage corresponds to memory 162 or 262.

The processing circuitry includes at least one of the exclusive hardwareand the program executing unit, and executes the processing using thestorage. In addition, when the processing circuitry includes the programexecuting unit, the storage stores a software program that is executedby the program executing unit.

Here, the software for implementing encoder 100, decoder 200, or thelike according to the present embodiment includes programs as indicatedbelow.

Specifically, a program may cause a computer to execute an encodingmethod of encoding video, the encoding method including: deriving aprediction error of an image included in the video by subtracting aprediction image of the image from the image; performing a primarytransform on the prediction error; performing a secondary transform onthe result of the primary transform; quantizing the result of thesecondary transform; encoding the result of the quantization as the dataof the image; and performing, when a current block has a predeterminedshape, the secondary transform using, among secondary transform basiscandidates that are secondary transform bases usable in the secondarytransform, only a secondary transform basis candidate having a size thatis not the largest size containable in the current block.

In addition, specifically, a program may cause a computer to execute adecoding method of decoding video, the decoding method including:decoding the data of an image included in the video; inverse quantizingthe data; performing an inverse secondary transform on the result of theinverse quantization; performing an inverse primary transform on theresult of the inverse secondary transform; deriving the image by adding,as a prediction error of the image, the result of the inverse primarytransform to a prediction image of the image; and performing, when acurrent block has a predetermined shape, the inverse secondary transformon, among secondary transform basis candidates that are secondarytransform bases usable in the inverse secondary transform, an inversesecondary transform basis candidate having a size that is not thelargest size containable in the current block.

In addition, each of the components may be the circuitry as describedabove. The circuitry may be configured as a single circuit as a whole,or as separate circuits. In addition, each of the constituent elementsmay be implemented as a general purpose processor or as a dedicatedprocessor.

In addition, processes executed by a specific component may be performedby a different component. In addition, the order in which processes areperformed may be changed, or a plurality of processes may be performedin parallel. In addition, an encoder/decoder may include encoder 100 anddecoder 200.

The ordinal numbers such as first, second, etc. used for explanation maybe arbitrarily replaced. In addition, an ordinal number may be newlyadded to a given one of the components, or the like, or the ordinalnumber of a given one of the components, or the like may be removed.

Aspects of encoder 100 and decoder 200 have been described above basedon the embodiments. However, aspects of encoder 100 and decoder 200 arenot limited to the embodiments described above. The one or more aspectsof the present invention may encompass embodiments obtainable by adding,to the embodiments, various kinds of modifications that a person skilledin the art would arrive at and embodiments configurable by combiningcomponents in different embodiments within the scope of the aspects ofencoder 100 and decoder 200.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 2

As described in each of the above embodiments, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoder/decoder that includes both the image encoder and the imagedecoder. Other configurations included in the system may be modified ona case-by-case basis.

[Usage Examples]

FIG. 20 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an α value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 21 , that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 21 . Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 22 , metadata is storedusing a data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 23 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 24 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 23 and FIG. 24 , a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

[Other Usage Examples]

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 25 illustrates smartphone ex115. FIG. 26 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, digital video cameras, teleconference systems,electronic mirrors, etc.

REFERENCE SIGNS LIST

-   -   100 encoder    -   102 splitter    -   104 subtractor    -   106 transformer    -   108 quantizer    -   110 entropy encoder    -   112, 204 inverse quantizer    -   114, 206 inverse transformer    -   116, 208 adder    -   118, 210 block memory    -   120, 212 loop filter    -   122, 214 frame memory    -   124, 216 intra predictor (intra-picture predictor)    -   126, 218 inter predictor (inter-picture predictor)    -   128, 220 prediction controller    -   160, 260 circuit    -   162, 262 memory    -   200 decoder    -   202 entropy decoder

The invention claimed is:
 1. An encoder comprising: circuitry; andmemory, wherein, using the memory, the circuitry: derives a predictionerror of a current block of an image; performs, based on a size of thecurrent block, either i) a primary transform on the prediction error anda secondary transform on a result of the primary transform, or ii) aprimary transform on the prediction error and a secondary transform on apart of the result of the primary transform; quantizes a result of thesecondary transform; and encodes a result of the quantization.
 2. Anencoding method comprising: deriving a prediction error of a currentblock of an image; performing, based on a size of the current block,either i) a primary transform on the prediction error and a secondarytransform on a result of the primary transform, or ii) a primarytransform on the prediction error and a secondary transform on a part ofthe result of the primary transform; quantizing a result of thesecondary transform; and encoding a result of the quantization.
 3. Anon-transitory computer readable medium storing a bitstream, thebitstream comprising: a coded data of a current block on which adecoding process is performed by a decoder, the coded data including afirst parameter according to which the decoder selects a second inversetransform basis from among second inverse transform basis candidates,wherein the decoding process comprises: inverse quantizing quantizedcoefficients of the current block; performing, depending on a size ofthe current block, either (i) an inverse secondary transform on a partof a result of the inverse quantization and an inverse primary transformon a result of the inverse secondary transform and another part of theresult of the inverse quantization, or (ii) the inverse secondarytransform on the result of the inverse quantization and the inverseprimary transform on the result of the inverse secondary transform; andderiving an image based on a residual signal derived from a result ofthe inverse primary transform.